Tuesday, July 05, 2016

Ballistas, Catapults and Scorpions

A major source of information for Roman artillery is Marcus
Vitruvius Pollio, a 1st century BC Roman author, architect, civil and military engineer. Commonly known as Vitruvius, Book X of his multi-volume work entitled DeArchitectura includes
chapters on artillery. In Book X.xvi.1,
for example, Vitruvius refers to three separate terms for siege machines when beginning
his description of the “Measures of Defence”.
Vitruvius (X.x.6) also claims to have described catapultorum rationes ("the rules of catapults") at the
end of the section on the scorpio,
which once again suggests a distinction.

For several years I accepted that catapults (bolt-shooters)
were synonymous with “scorpions” following Vitruvius, and have even described
them as such using the analogy of the bolt being the scorpion’s “sting in the
tail”. In the opening of Book X, Chapter
x, for example, he writes of “catapults or scorpiones”
and then in the first paragraph refers to “scorpiones
and ballistae (X.x.1). If Vitruvius’ use of terminology is
inconsistent, then it is more confusing wherever he makes a distinction between
three types of machine, i.e. ballistas, catapults and scorpions.

Yet Vitruvius is not alone.
The Roman encyclopaedist Pliny the Elder(HN
7.201) also lists the three machines separately[1], and Livy (26.47),
in his catalogue of Carthaginian machines captured at New Carthage in 209 BC,
writes of:

"120 catapults of the
largest dimensions, 281 smaller ones; 23 larger ballistas, 52 smaller ones;
larger and smaller scorpions and a huge number of weapons and projectiles"

Is it possible, therefore, that these authors considered the
scorpion a distinctly different machine from a stone-throwing ballista or a
bolt-shooting catapult. If so, then what
did this other scorpion look like?

For our purposes, ballistae,
catapultae, and scorpiones are all torsion based artillery. The principle of torsion was probably
discovered by artificers working in Macedonia under Philip II and Polyidus
between 353 BC and 341 BC. Our understanding
of their construction comes from Heron’s description (Belopoiika 81): “two separate wooden arms were inserted into two
vertical skeins or springs of sinew-rope mounted in a stout frame of hardwood
reinforced with iron plates. Each strand
of the rope is pre-stretched by winches around top and bottom iron
washer-bars. The iron washer-bars were
slotted into revolving bronze cylinders that allowed the skein to be twisted,
forcing the bow arms forward. This
twisting or torsion of the rope-springs was further increased when the arms
were drawn back by winch, storing a massive amount of potential energy in the
sinew.”[2]

When it comes to stone-throwers (Gr. lithobolos (Λιθοβόλος))
and bolt-shooters (Gr. OxybelesΟξυβόλος)), the former are described as euthytonon (or euthytone), while the
latter are palintonon (or palintone).
In Greek, a palintonon translates as "V-spring" and euthytonon (Ευθύτονος) translates as "straight-spring". The "V" or straight spring describes
how the construction of the spring frames and the shape of the bow arms of siege
engines compare to shape of hand-held bows.

Confused? In the
early Imperial period, as under the Republic, two types of artillery were
known: bolt-shooting euthytones (the scorpiones
and catapultae of Vitruvius’ De Architectura X, x, 1-6) and stone-throwing
palintones (the ballistae of
Vitruvius’ De Architectura X, xi,
1-9). According to Marsden these
machines were apparently allocated 55-60 per legion[3]. Yet by the fourth century AD it seems the
legions had lost their organic complement of artillery and the term ballista (and its compounds) appears in
the literary sources to refer to an iron-framed bolt-shooter. Presumably this was because the engine was
technically a palintone, not a euthytone, and the old wooden-framed stone-throwing
ballista is replaced by the more
massive one-armed onager (Vegetius, Epitoma
Rei Militaris ii, 10, 15 and 25; iii, 14 and 24; iv, 22).

Ammianus Marcellinus concurs. By the mid-4th century AD, the Romans were
employing the one-armed onager as their stone-projector, while the ballista
seems to have been used only as a bolt-shooter, a task previously given to the
euthytone, i.e. catapults. Most
importantly, Ammianus (23.4.7) claims that the onager had previously been known
as a “scorpion”, quoniam aculeum desuper
babet erectum ("because it has its sting raised up above it")[4].

Yet the 4th century AD is by no means the first
appearance in the surviving literary sources for one-armed stone-throwing
machines. In c. 210 BC, some 500 years
earlier, Philon of Byzantium casually refers to just such machine in his
treatise on siegecraft, Poliorketika,
in a passage concerned with defending a city under siege[5]. Had the one-armed stone-thrower been “hidden
in plain sight” serving alongside the other named machines since Philon’s
time? Could the separate references to
“scorpions” be the very same machines or their descendents for example the
later Roman onager of Ammianus and Vegetius?

The design of the onager
as a mechanized staff-sling is often thought to have been a late development,
but as we have already seen Philon was aware of one-armed stone-throwers. Unfortunately, he provides no specifics, and the
weapon’s construction from mostly organic materials means that few physical
remains are likely to survive. Scroll
forward just over three centuries later and a fleeting reference to a one-armed
stone-thrower next appears in the work of the Emperor Trajan's engineer,
Apollodorus of Damascus. Indeed, the
time of Trajan’s reign is significant because, as Marsden determined, during
this period the terminology for artillery clearly changed.

Marsden was struck by the similarities between
Heron’s cheiroballistra, an
iron-framed palintone bolt-shooter, and the artillery pieces depicted on
Trajan’s Column in Rome that date to around AD 110. Although they were bolt-shooters, their wide
palintone torsion frames qualified them for the term ballistae. It seemed clear
to Marsden that, from the reign of Trajan onward, palintones supplanted
euthytones as the preferred machines for shooting bolts; ironically a
capability they had always possessed. The
euthytone design seemingly disappeared from the mainstream and the
one-armed machine usurped the name scorpio
(scorpion), which had, up to this point, indicated a euthytone bolt-shooter.

If more evidence is needed then in his Scorpiace, written ca. AD 210,
Tertullian describes how the creature, "rising up in an arching attack,
draws its hooked sting up like a torsion machine; from this feature, they call
the war machine a scorpion, that shoots its missiles by retracting."[6] Tertullian equates the scorpion's tail to a
one-armed torsion machine of the same name, in exactly the same way that Ammianus
will do later.

Despite Tertullian from the reign of Emperor Trajan
until the fourth century AD, when they are familiar to Ammianus and Vegetius, it seems that “the one-armed machines slip once more into obscurity.”[7] Marsden notes that Ammianus refers to these
one-arm machines as scorpio, catapulta, or onager, although Ammianus gives us the impression that the latter
name was the “modern” and popular one.

So, what can we conclude? The name applied to a given piece of
torsion artillery heavily depends which author you reference, their familiarity
with the subject matter, and the point in time they are describing. It is just possible that all three types of weapon
were in use concurrently and that perhaps the terms catapult, ballista and
scorpion did refer to bolt-shooters, stone-throwers and one-armed machines
respectively. Personally, the author is
inclined to use the terms catapultae for
bolt-shooting euthytones, ballistae
for stone-throwing palintones and, like Tertullian, reserve the term scorpiones for the one-armed machines
known to later Romans as “onagers”. But then, what's in a name?

Notes:

1. Pliny the
Elder, The Natural History, Book VII, 201: “...among the artillery, the
scorpion [were invented by[ the Cretans, the catapult [by] the Syrians, the
ballista and the sling [by] the Phoenicians.”

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We are historical interpreters and presenters who teach in schools and colleges, deliver living history demonstrations at events across Great Britain, and carry out reconstructive or experimental archaeology to better understand the lives of our forebears.